Mitochondria are the organelles of the living cell that contain several (but not all) of the protein pathways of metabolism, including the citric acid cycle and the electron transport chain. They are responsible for a variety of metabolic processes including fatty acid metabolism and pyruvate oxidation, while pyruvate is produced outside of the mitochondria from glycolytic pathway oxidation of sugars.
The citric acid cycle is a key metabolic pathway that unifies carbohydrate, fat, and protein metabolism. The reactions of the cycle are carried out by enzymes that completely oxidize acetate, in the form of acetyl-CoA, into two molecules each of carbon dioxide and water. Through catabolism of sugars, fats, and proteins, a two-carbon organic product acetate in the form of acetyl-CoA is produced which enters the citric acid cycle.
The reactions of the cycle also convert three equivalents of nicotinamide adenine dinucleotide (NAD+) into three equivalents of reduced NAD+ (NADH), one equivalent of flavin adenine dinucleotide (FAD) into one equivalent of FADH2, and one equivalent each of guanosine diphosphate (GDP) and inorganic phosphate (Pi) into one equivalent of guanosine triphosphate (GTP).
Biological supercapacitors harness the catalytic activity of living cells, which are able to conduct electrochemical reactions and produce electrical energy. When using biological materials as catalysts at the anode or cathode of a biological supercapacitor, the catalyst needs to be immobilized at the surface of the electrode.
In its most general aspect, a biological supercapacitor consists of paired electrodes and on one side of the interface a layer of electrons forms. On the opposite side of the interface, a layer of positive ions forms. Together, these two layers are the double layer, which store energy.
The voltage across the interface increases with charge accumulation. In connection with the double layer capacitance phenomenon, no charge transfer (Faradaic) process occurs at the electrode/electrolyte interface. During discharge, the charge stored at the interface is released. The charge/discharge rate is generally determined by the nature and type of the material, its thickness, and the electrolyte.